Annular linear flow electromagnetic induction pumps for impelling liquid metals generally comprise an annular flow channel or duct which is surrounded by a stator column composed of a multiplicity of alternating annular coils and magnetic iron rings. This type of electromagnetic pump, commonly known as a single-stator, annular linear-flow induction pump, and its use in a liquid metal-cooled nuclear fission reactor, are disclosed in U.S. Pat. Nos. 4,859,885 and 4,882,514.
However, a more versatile linear-flow electromagnetic induction pump design than those shown in the above patents comprises a double-stator system. This electromagnetic pump system comprises an outer stator arrangement surrounding the outer flow duct of an annular flow channel and an inner stator arrangement concentric with the outer stator and enclosed within the inner duct of the annular flow channel. The inner and outer stator columns are each composed of a multiplicity of alternating annular coils and iron lamination rings. In combination, the outer and inner, or double, stators act upon the liquid metal flowing linearly through the annular flow duct.
This double-stator pump design provides greater pumping capacity per pump unit size, or alternatively equal capacity provided by a smaller pump unit. Accordingly, among the advantages of the double-stator pump are greater efficiency and versatility.
In the single-stator design, the stator column surrounds the outer flow duct of the annular flow channel. Because the outer flow duct is made of metal having a thermal expansion coefficient greater than that of the carbon steel of the lamination rings therearound, the outer flow duct expands radially outward more than the lamination rings expand, causing the outer flow duct to exert a radially outward clamping force on the lamination rings.
However, when the lamination rings are radially inward of the inner flow duct, as is the case for the double-stator design, the tendency--in the absence of remedial measures--is for radial clamping by the inner flow duct to be lost as the inner stator is brought up to operating temperature. In addition to radial clamping, means for axially and circumferentially clamping the coils and lamination rings of the inner stator structure must be provided.